It really doesn't matter about his regret. The deed was done. He served his master at the time and his deeds are recorded in history. I'm not excusing him just like I'm not excusing any White person who has engaged in White Supremacy all their lives and has just recently become an antiracist. They hurt people along the way being racist and anti-Black, some folks were likely irreparably damaged. Because they are new people now, it doesn't erase the sin.
The sin is done and it needs to be a part of history. It can be used as an example for Blacks anywhere illustrating how we cannot trust White Supremacy and how it plays both sides. We must have integrity and stay on code regardless of political ideologies. Robinson made a terrible mistake but it cost Roebson more. Jackie Robinson "felt" bad, while Paul Roebson lost his livelihood, liberties, and was labeled. When you bring up his feelings to me it's a cop-out. Robinson could've said no but he didn't. He made a bad choice and it did harm to the entire race.
It's a perfect example of how certain classes of Black people can't be trusted. They'll throw us under the bus, live a good life, then spend the rest of their days regretting it. Regret means nothing when someone's livelihood has been ruined.